Until long haul fiber optic systems were developed there was not much call for loss localization over great distances. Even when the land based telecommunications community used long lengths of optical fibers it was much easier to localize faults than with undersea systems. For example, there was the practical problem of where a suspected fault is located when the fault location is being made relative to the world that we are all familiar with. For example, if a maintenance crew is told that an optical fiber is broken 13.123 kilometers down the line this information is of little use as they search exactly where the break is made. Familiar landmarks, odometer readings and lastly a tape measure provide some help however these can be impractical in a good many applications such as hilly or mountainous terrain.
Optical data transmission cables include optical fibers that typically are fabricated by drawing down a glass rod that contains a core region and cladding region. The resulting drawn fiber provides a transmission path for light energy. When such a fiber is bent some of the energy passes through the cladding and is absorbed by the fiber's coating. This creates a localized loss of light and is indicated by a reduction of the transmitted power. Different fibers and cable constructions have been noted as providing various magnitudes of loss for a given bend.
The optical time-domain reflectometer (OTDR) is a well known device for determining the transmission characteristics of a particular fiber. The losses attributed to bends can be localized and measured. It is not uncommon for off-the-shelve OTDRs to measure distances greater than 100 kilometers and resolve power to 0.01 db. As a consequence, it is well known that OTDRs have the capability of pin-pointing losses attributed to bends throughout the length of an optical fiber being measured.
When trying to determine where a particular location along a fiber cable is, a technician or optical fiber serviceman would simply kink or bend the fiber cable by hand and a distant observer would monitor where the kink or bend is located by an interconnected OTDR. Then the technician or workman could go one way or the other along the fiber cable to the point where a particular equipment or maintenance or servicing has been indicated as needing attention.
This is essentially the same routine relied upon when divers go along the length of an undersea fiber and try to help locate a fault or point where instrumentation is to be maintained or attached. When the diver's location is determined by noting where a bend is made in the fiber, appropriate instructions can be transmitted so that the diver can go to the desired place. One drawback of this approach is that, despite the ruggedness and the adaptability of optical fibers for a wide variety of data gathering tasks, the fibers can be damaged when bent or crimped too hard. An inadvertent extreme bending, in the case of a particular fiber, may cause cracks or otherwise damage the fiber to impair its data transmission capabilities. This undesirable consequence should be avoided whenever and wherever possible. An alternative to this way of determining a precise location along an undersea cable would be to measure the distance physically. Under water this would require substantial diver time or a very good underwater vehicle. A satellite location device may also provide general location and acoustic navigational aids may also be relied upon. However, none have the accuracy for precisely determining location along a cable's length.
Thus, a continuing need exists in the state of the art for a calibrated bender for an optical fiber which provides for the location of a series of predetermined bends that do not damage the fiber yet assures the precise location of the bends by a remote OTDR.